Energy efficient data transmission

ABSTRACT

A method and apparatus for data transmission at energy efficient rates. An embodiment of an apparatus includes a port for the transfer of data. The port has an active state in which the port may transmit or receive data and an inactive state in which the port does not transmit or receive data. The apparatus further includes logic to control the transfer of data. The logic places the port into the active state for a first time period for the transfer of data and places the port into the inactive state for a second time period. The logic further prevents transfer of data during the inactive state.

FIELD

An embodiment of the invention relates to data communication in general,and more specifically to data communication at energy efficient rates.

BACKGROUND

In computer data communications, there is often a trade-off betweendesired outcomes. In one example, the performance of a system is oftenbalanced against power consumption. In common computer systems, moreoverall power is consumed when the speed of operation is increased. Forthis reason, increasing performance in the speed of transmission of datawill generally have costs in the consumption of power and, as a result,in the generation of excess heat. The power utilization of componentshas become increasingly important to manufacturers as computers andother electronic devices become smaller and more powerful, thusimplicating issues of energy costs, battery size and life, and thermalconsiderations to dissipate heat.

In order to minimize power consumption and heat generation, theoperation of a conventional computer component or other device willoften be reduced to a minimally acceptable speed. This sacrifice ofperformance is particularly important in mobile operations in which thepower source is a battery or other portable power generation or storagedevice. If power usage is reduced, then greater length of operation maybe possible, a smaller and lighter battery may be useable, andadditional heat dissipation measures may be avoided.

However, the increasing speed of communications and computer operationsand the increasing data loads faced by systems make the tradeoff betweenpower consumption and speed of data transmission more difficult, andthus sacrificing the performance of a system may be not acceptable. Ifother possible power savings measures are in place, then a reduction inspeed in data transmissions may further reduce power consumption andheat generation, but only at the cost of insufficient systemperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention may be best understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 is an illustration of an embodiment of data communicationsbetween elements;

FIG. 2A is a table to illustrate power consumption of an exemplarydevice at varying link speeds;

FIG. 2B is a graph to illustrate power consumption of an exemplarydevice at varying link speeds;

FIG. 3 is an illustration of a system to transfer data at an energyefficient link rate under an embodiment of the invention;

FIG. 4 is a flowchart to illustrate a method for transmitting data at anenergy efficient rate under an embodiment of the invention;

FIG. 5 is an illustration of energy costs of various link speeds for adevice in an embodiment of the invention; and

FIG. 6 is an illustration of an embodiment of a computer system.

DETAILED DESCRIPTION

A method and apparatus are described for communication at energyefficient rates.

In one embodiment of the invention, a component transfers data at aparticular data rate and then transitions to a low power inactive statewhen not transmitting data. In an embodiment of the invention, thecomponent reduces energy consumption by sleeping and preventing any datatransmission during inactive periods.

In an embodiment of the invention, a component may choose a data ratebased on efficiency in terms of energy consumed per unit of datatransferred. In one embodiment, a component chooses the most energyefficient link speed for a data transmission.

In an embodiment of the invention, a component may notify an operatingsystem (OS) regarding an effective rate of data transmission. In anembodiment, the effective rate of data transmission is based at least inpart on the current link speed and the ratio between active time periodsand inactive time periods for data transmission.

For the transfer of data, the consumption of power in terms of Watts (orJoules of energy per second) may be less important than the consumptionof energy in terms of energy per unit of data, such as in terms ofJoules of energy expended per bit of data transferred. This is truebecause energy usage of a device is not generally linear with respect tolink speed. While energy usage generally increases with link speed, theenergy usage does not necessarily increase at the same rate as the linkspeed. For this reason, there may be a link speed for a device that ismore efficient than other link speeds in that the device consumes theleast amount of energy per bit of data using the chosen link speed.Under an embodiment of the invention, a device may determine and utilizethe most efficient available link speed for a transmission.

For the purposes of an embodiment of the invention, energy efficiencydetermination may take into account various factors. For example, theenergy efficiency determination may include energy consumed by anelement when the device is actively transmitting data, when the elementis in a low power inactive state between data transmissions, and whenthe element is transitioning between active and inactive states. In anembodiment, the energy efficiency may be based on the total energy costof a device during a time period.

Under an embodiment of the invention, a component may include, but isnot limited to, an I/O (input/output) controller or similar I/Ocomponent or element of a computing system. The transmission of data mayutilize, but is not limited to, Ethernet technology, and may include MAC(media access controller), PHY (physical line or media interface), orcombined MAC/PHY Ethernet elements. The component may include logic tocontrol data transmission processes and may include one or more portsfor the transmission of data. Under an embodiment of the invention, acomponent may support multiple different data transmission rates, withthe rates varying in efficiency in terms of energy consumed per unit ofdata transferred. In one example, a device may include a10/100/1000BASE-T Gigabit Ethernet device that includes ports thatsupport speeds of 10 Mbps (megabits per second), 100 Mbps, and 1000Mbps. In an embodiment in which a component has multiple link speeds,the component logic may select the most energy efficient link speed thatis available. While this description generally refers to a component,the component may be any element, apparatus, system, platform, orcombination of elements.

In most cases the most efficient data transmission rate for a componentwill be the fastest link speed that is supported by both thetransmitting device and the receiving device under the circumstances. Inthis way, a choice of the most efficient available link speed may alsomaximize the speed of transmission for the current conditions. However,embodiments of the invention are not limited to use of the fastestavailable link speed, and will relate to the choice of any energyefficient link rate regardless of the applicable link rate.

Under an embodiment of the invention, a determination regarding a linkspeed may be made based at least in part on the amount of energyexpended for the transmission of a given amount of data (as expressedin, for example, Joules of energy per bit of data). In an embodiment,the component will transmit data at the selected rate and thentransition to a low power inactive state, such as a deep sleep state,until more data is to be transmitted.

In one embodiment of the invention, a component will prevent a linkpartner from engaging in any I/O activity during an inactive timeperiod, which allows the component to sleep. There are multiple methodsby which the link partner may be instructed to refrain from activity indifferent embodiments of the invention. In one possible embodiment,pause frames may be used, such as IEEE 802.3x pause (XOFF) frames (IEEE,Specification for 802.3 Full Duplex Operation and Physical LayerSpecification for 100 Mb/s Operation on Two Pairs of Category 3 orBetter Balanced Twisted Pair Cable (100BASE-T2), 1997; and later 802.3specifications, including 1998 and 2000). While the link partner ispaused, the component can go into a low power inactive mode.

In one embodiment of the invention, a component will batch data packetstogether to transmit during active periods. For example, data packetstransmit requests occurring during an inactive period may be queued andbe held until the component transitions to the active mode, at whichtime all the queued packets may be sent.

In one embodiment of the invention, a component transitions to a lowpower state during inactive periods. If the inactive state for a higherspeed has sufficiently low power consumption requirements, then theoverall power consumption over a cycle of active mode data transfers andinactive mode sleep will be less than the power consumption that wouldresult from running the component at a slower link speed. In oneembodiment, the low power inactive state is a deep sleep state in whichthere are no I/O activities. In one embodiment, the low power state is astate that reduces the power consumed to a lower level, but thatmaintains a link between the transmitting component and the receivingcomponent. However, embodiments of the invention are not limited to anyparticular low power implementation and may operate with any state thatconsumes less power than the active state of the transmitting component.Various different types of low power or sleep states or modes may beavailable for various components and system technologies.

In one embodiment of the invention, a component reports a link speed toan operating system, with the reported link speed reflecting aneffective rate of data transmission rather than the actual link speed.In an embodiment, the effective rate of transmission takes into accountthe current duty cycle of the component, the duty cycle reflecting thepercentage or proportion of time that the component is active versusinactive. In an embodiment, an effective rate of data transmission maybe calculated as the link speed times the proportion of time in whichthe component is active. For example, if the link speed is 1 Gb persecond while the current duty cycle is 5 percent (the component isactive 5 percent of the time and in a low power inactive state 95percent of the time), then the effective rate of transmission is0.05×1000 Mb per second=50 Mb per second. In this example, the componentreports a link speed of 50 Mbps to the operating system. The operatingsystem then can use the reported link speed for data expectations andavoid confusion regarding the actual throughput at a given link speed.

In an embodiment of the invention, the transmission duty cycle for acomponent may be adjusted as needed. For example, if too much data isbuffered before transmission to allow all of the data to be transferredduring the active portion of the duty cycle, then the active portion ofthe duty cycle may be increased to allow batched packets to betransmitted during the active portion of a duty cycle. Similarly, if theamount of data presented for transmission is small, then the activeportion of the duty cycle may be reduced to further reduce the length oftime that the component is active and thus further reduce the totalpower consumption of the device.

In an embodiment of the invention, data transmission may include thefollowing processes:

(a) Receiving data for transmission between a component and a linkpartner. The received data packets may be held during an inactive timefor sending in a batch process in an active period.

(b) If multiple link speeds are available, selecting the most energyefficient link speed that is available for the transmission between thecomponent and the link partner. If the link speeds become more efficientas they increase, then the most energy efficient link speed would be thefastest link speed supported by both the component and its link partner.

(c) Reporting a link speed to the operating system that is consistentwith what the expected data throughput will be for the current dutycycle.

(d) Transferring data at the chosen link speed.

(e) When the active period for the component has ended, preventing thelink partner from sending additional data packets to allow the componentto remain dormant for a certain amount of time.

(f) Transitioning the component to a low power inactive (or sleep) modewith no I/O transfers occurring during this period.

(g) Returning to an active mode of operation for additional dataoperations.

(h) Adjusting the duty cycle as needed depending on the currentconditions.

FIG. 1 is an illustration of an embodiment of data transmission betweenelements. In this illustration, a first component 105 is transmittingdata to or receiving data from a second component 110. The firstcomponent 105 and the second component are elements of some system orapparatus, such as a computer. The first component 105 may include logic140 to control data transmission and may include one or more ports 145for the transmission of data. The first component 105 may be capable oftransferring data at various different link speeds 115, represented byspeed a, b, c, and d, and the second component 110 may be capable ofreceiving data at various different link speeds, represented by speedsa, b, and c. The link speeds supported by each component are notnecessarily the same. In this illustration, the first component 105 willtransmit data 125 to the second component at a link speed that issupported by both components.

In an embodiment of the invention, the first component 105 transfersdata to the second component 110 during an active state, and thentransitions to an inactive state during which no data is transferredbetween the components. To reduce the power consumption 130, theinactive state is a low power state, such as a sleep state, that may beutilized when not transmitting data. In an embodiment of the inventionin which there are multiple possible link speeds, the first componentmay transfer data 125 at the available link speed 115 that mostefficiently transfers the data in terms of energy per unit of data. Inthis manner, the first component reduces the power consumption 130 ofthe system and potentially reduces the excess heat production 135 of thesystem.

FIG. 2A is a table to illustrate power consumption of an exemplarydevice at varying link speeds. While this table shows the results for aparticular device with certain characteristics, embodiments of thisinvention are not limited to these characteristics and can be applied toany device that has varying energy requirements for different speed orclock settings. In this illustration, it can be seen that the powerconsumed by the device increases with the link speed setting. For activeoperation, the power consumed rises from 250 power units at 10 Mb persecond to 1500 units at 1000 megabits per second. There is a reductionof power consumed when the device is at idle, but, for this particulardevice, the reduction is not significant, such as a reduction from 1500units to 1300 units when the device is active versus idle at a linkspeed of 1 gigabit per second. For this reason, a conventional systemmay reduce the link speed to save power and further to reduce excessheat production. For instance, the active power consumption at 100 Mbper second is still less than the idle power consumption at 1000 Mb persecond and thus a convention system may run at 100 Mb per second toconserve power.

However, it can also be seen that, while the total power consumption isgreater as the link speed increase, the energy that is consumed inactive operation when measured as energy per unit of data transferred,such as in terms of Joules per bit, actually decreases as the link speedincreases. The reason for this is that the increase is power as linkspeed increases is not linear for this device. Under an embodiment ofthe invention in which there are multiple available link speeds, asystem may select the most efficient available link speed for a devicein terms of energy per unit of data transferred and transfers data usingthis link speed.

FIG. 2B is a graph to illustrate power consumption of an exemplarydevice at varying link speeds. The illustrated graph provides a diagramof the characteristics of the device that provides the results shown inFIG. 2A. As shown in this logarithmic scaled graph, the power consumedat the differing link speeds is increasing as link speeds increase.While the total power consumed is increasing, conversely the energyconsumed in terms of energy per bit is actually decreasing. Under anembodiment of the invention, a system utilizes the characteristics of aspecific device to transmit at the most energy efficient rate that isavailable for the device under the circumstances.

FIG. 3 is an illustration of a system to transfer data at an energyefficient link rate under an embodiment of the invention. In thisillustration, a first element 305 is communicating with a second element310. The first element 305 may include logic 350 to control datatransfer processes by the element and may include one or more ports 355for the transmission of data. In one embodiment of the invention, thesystem transfers data efficiently by transferring data during an activeperiod and sleeping during a low power inactive period. In an embodimentof the invention, the first element prevents any data transferenceduring the inactive period.

In one embodiment of the invention, the system may include multiple linkspeeds. The system may select a link speed from the multiple linkspeeds. The selection of the link speeds may vary with the particularembodiment. In one embodiment, the data efficiency of the link speedsmay be a part of the logic 350 of the first element. In anotherembodiment, information regarding energy efficiency may be contained inanother location, such as, for example, data regarding the efficiency oflink speeds 335 contained in a memory, register, or other data storage330. In an embodiment, the system selects a link speed based the energyefficiency of each available link speed. For example, the first element305 and the second element 310 may communicate at a link speed 315 and320 that is the most energy efficient link speed available for suchelements, shown as link speed c in this example.

In an embodiment of the invention, a link speed is reported 340 to theoperating system 345. The reported link speed 340 is generally not theactual link speed, but rather reflects an effective link speed based onthe speed of transmission and the current duty cycle of the datatransmission, the duty cycle representing the relative time periods foractive and inactive modes. The reported link speed 340 reflects theexpected data throughput for the system, and thus will reflect the datarate that the operating system 345 will be expected to see.

FIG. 4 is a flowchart to illustrate a method for transmitting data at anenergy efficient rate under an embodiment of the invention. In anembodiment of the invention, data is transferred between a component anda link partner. The component may comprise, for example, an I/Ocontroller transmitting and receiving data via Ethernet technology. Inone embodiment, the component may have multiple available link speedsand a link speed may be selected based on the relative energy efficiencyof the link speeds 405, with the efficiency of each link speed beingdetermined based at least in part on the energy expended per unit ofdata transferred. In addition, an effective link speed based on theactual link speed and the current duty cycle of the system is reportedto the operating system 410. Assuming that the component begins in aninactive state, data may be received for transmission and queued 415.The component is then put in an active mode for operation 420. Datapackets are then sent and received at the selected link speed 425.Following the transmission, the link partner and any program filters arepaused to allow the transmitting element to sleep between transmissionsand thus to wait for more data for transmission at the more energyefficient link speed 430.

The system may then enter a low power inactive mode, putting the firstcomponent into an inactive (or sleep) mode 435. The inactive operationmay include putting both the MAC and PHY elements (if applicable) into asleep state. In an embodiment of the invention, the inactive mode is adeep sleep mode that minimizes the use of power when the element is notactively sending or receiving data. In an embodiment of the invention,the sleep mode maintains a transmission link to reduce the amount oftime required to bring the system back to an active and ready status,but embodiments of the invention are not limited to such a sleep mode.

There may be a determination whether an adjustment in the datathroughput is needed or desirable 440. If not, the system may return thetransmission cycle, such as in receiving more data for transmission 415.If an adjustment in data throughput is needed, then an adjustment in thetransmission duty cycle is made 445, which may increase or decrease theproportion of time that data is transmitted versus the proportion oftime that the element is inactive in a sleep state.

FIG. 5 is an illustration of energy costs of various link speeds for adevice in an embodiment of the invention. The illustrated table providesexamples for a particular device transferring data at three link speeds(10 Mbps, 100 Mbps, and 1 Gbps) in a conventional operation and at alink speed of 1 Gbps for a transmission including an inactive sleep modeunder an embodiment of the invention. In this illustration, the totalenergy expended to transmit data may be composed of the Transfer Energy(the energy needed to transfer the data), plus idle time (the energyused in an idle state when not transferring data) and pause andtransition energy (energy expended in connection with pausingtransmission activities and transitioning to and from a sleep state).The time to transmit data is composed of the Data Transfer Time (thetime expended in actually transferring the data), plus the PauseTransfer Time and Power Transition Time (time for pausing transmissionactivities and for transitioning to and from a low power inactivestate).

As shown in FIG. 5, the data transfer rate may vary from 8.75milliseconds at a link speed of 1 Gbps to 875 milliseconds at a linkspeed of 10 Mbps. For the 1 Gbps link speed, the transfer energy is only13 energy nits, but the idle time consumes additional energy units. Inthis example, the transfer energy for the data increases as the linkspeed is reduced, but the idle energy would be reduced with thereduction in link speed and thus the total energy may be reduced.Therefore, in a conventional system the link speed may be reduced tominimize the energy expended by the system.

However, under an embodiment of the invention, the total energy may bereduced by choosing the link speed that has the best efficiency in termsof energy per unit of data transferred. In FIG. 5, the most efficienttransfer link speed is 1 Gbps, which expends only 13 units for the datatransfer in this example. To this would be added the energy expended forpausing and for transition to a low power state and the energy expendedin the low power state, which may be significantly less than the energyconsumed by a device in an idle state. The total energy consumed thusmay be reduced. The example provided reflects an exemplary device havingcertain characteristics and being transitioned to a very low power sleepstate. Embodiments of the invention are not limited to elements havingany particular characteristics, and may be used with a variety ofdifferent types of devices with varying power consumption properties.The choice of the most energy efficient link speed could vary dependingon the energy expended for pause and transition operation and for idleoperation because the most efficient link speed for transferring datamay not be the most efficient when considering the total energyexpenditure by the device.

FIG. 6 is an illustration of an embodiment of a computer system. Underan embodiment of the invention, a computer 600 comprises a bus 605 orother communication means for communicating information, and aprocessing means such as two or more processors 610 (shown as a firstprocessor 615 and a second processor 620) coupled with the bus 605 forprocessing information. The processors 610 may comprise one or morephysical processors and one or more logical processors. Further, each ofthe processors 610 may include multiple processor cores. The computer600 is illustrated with a single bus 605 for simplicity, but thecomputer may have multiple different buses and the component connectionsto such buses may vary.

The computer may further include an I/O controller 622 to control inputand output transactions. Under an embodiment of the invention, the I/Ocontroller 622 of the computer 600 may transfer data at varying clockspeeds. Under an embodiment of the invention, the computer willdetermine the most energy efficient available transmission speed interms of Joules of energy per unit of data transferred. Under anembodiment of the invention, the I/O controller 622 will transfer dataat such rate and enter a deep-sleep mode in time periods when nottransferring data. Under an embodiment of the invention, the computer600 will report an effective data transfer rate to an operating systemof the computer 600 for the current duty cycle of data transfer andsleep periods, the duty cycle representing the relative time period forthe data transfers and sleep operations.

The computer 600 further comprises a random access memory (RAM) or otherdynamic storage device as a main memory 625 for storing information andinstructions to be executed by the processors 610. Main memory 625 alsomay be used for storing temporary variables or other intermediateinformation during execution of instructions by the processors 610. Thecomputer 600 also may comprise a read only memory (ROM) 630 and/or otherstatic storage device for storing static information and instructionsfor the processors 610.

A data storage device 635 may also be coupled to the bus 605 of thecomputer 600 for storing information and instructions. The data storagedevice 635 may include a magnetic disk or optical disc and itscorresponding drive, flash memory or other nonvolatile memory, or othermemory device. Such elements may be combined together or may be separatecomponents, and utilize parts of other elements of the computer 600. Thedata storage device 635 may include stored data regarding the energyefficient of the link speeds supported by the I/O controller 622.

The computer 600 may also be coupled via the bus 605 to a display device640, such as a cathode ray tube (CRT) display, a liquid crystal display(LCD), a plasma display, or any other display technology, for displayinginformation to an end user. In some environments, the display device maybe a touch-screen that is also utilized as at least a part of an inputdevice. In some environments, display device 640 may be or may includean audio device, such as a speaker for providing audio information. Aninput device 645 may be coupled to the bus 605 for communicatinginformation and/or command selections to the processors 610. In variousimplementations, input device 645 may be a keyboard, a keypad, atouch-screen and stylus, a voice-activated system, or other inputdevice, or combinations of such devices. Another type of user inputdevice that may be included is a cursor control device 650, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to the one or more processors 610 andfor controlling cursor movement on the display device 640.

A communication device 655 may also be coupled to the bus 605. Dependingupon the particular implementation, the communication device 655 mayinclude a transceiver, a wireless modem, a network interface card, LAN(Local Area Network) on motherboard, or other interface device. In oneembodiment, the communication device 655 may include a firewall toprotect the computer 600 from improper access. The computer 600 may belinked to a network or to other devices using the communication device655, which may include links to the Internet, a local area network, oranother environment. The computer 600 may also comprise a power deviceor system 660, which may comprise a power supply, a battery, a solarcell, a fuel cell, or other system or device for providing or generatingpower. The power provided by the power device or system 660 may bedistributed as required to elements of the computer 600. Under anembodiment of the invention, the drain of power from the power device660 of system may be reduced by utilizing the most efficient link speedfor the I/O controller 622 in terms of Joules of energy consumed fromthe power device or system 660 per unit of data transferred.

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of embodiments of the present invention. It will beapparent, however, to one skilled in the art that the embodiments of thepresent invention may be practiced without some of these specificdetails. In other instances, well-known structures and devices are shownin block diagram form.

Embodiments of the invention may include various processes. Theprocesses of embodiments of the invention may be performed by hardwarecomponents or may be embodied in machine-executable instructions, whichmay be used to cause a general-purpose or special-purpose processor orlogic circuits programmed with the instructions to perform theprocesses. Alternatively, the processes may be performed by acombination of hardware and software.

Portions of embodiments of the invention may be provided as a computerprogram product, which may include a machine-readable medium havingstored thereon instructions, which may be used to program a computer (orother electronic devices) to perform a process according to embodimentsof the invention. The machine-readable medium may include, but is notlimited to, floppy diskettes, optical disks, CD-ROMs (compact diskread-only memory), and magneto-optical disks, ROMs (read-only memory),RAMs (random access memory), EPROMs (erasable programmable read-onlymemory), EEPROMs (electrically-erasable programmable read-only memory),magnet or optical cards, flash memory, or other type ofmedia/machine-readable medium suitable for storing electronicinstructions. Moreover, embodiment of the invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer to a requesting computer by way ofdata signals embodied in a carrier wave or other propagation medium viaa communication link (e.g., a modem or network connection).

Many of the methods are described in their most basic form, butprocesses can be added to or deleted from any of the methods andinformation can be added or subtracted from any of the describedmessages without departing from the basic scope of embodiments of theinvention. It will be apparent to those skilled in the art that manyfurther modifications and adaptations can be made. The particularembodiments are not provided to limit embodiments of the invention butto illustrate such embodiments. The scope of embodiments of theinvention is not to be determined by the specific examples providedabove but only by the claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of embodiments of theinvention. Similarly, it should be appreciated that in the foregoingdescription of exemplary embodiments of the invention, various featuresof embodiments of the invention are sometimes grouped together in asingle embodiment, figure, or description thereof for the purpose ofstreamlining the disclosure and aiding in the understanding of one ormore of the various inventive aspects. This method of disclosure,however, is not to be interpreted as reflecting an intention that theclaimed invention requires more features than are expressly recited ineach claim. Rather, as the following claims reflect, inventive aspectslie in less than all features of a single foregoing disclosedembodiment. Thus, the claims are hereby expressly incorporated into thisdescription, with each claim standing on its own as a separateembodiment of this invention.

1-28. (canceled)
 29. A method comprising: at a first Ethernet link partner coupled by an Ethernet link to a second Ethernet link partner: causing a PHY of the first Ethernet link partner to enter a lower power state from an active state, wherein the lower power state consumes less power than the active state but maintains the Ethernet link between the first Ethernet link partner and the second Ethernet link partner; enqueuing data packets for transmission to the second Ethernet link partner via the link while in the lower power state; and transmitting the enqueued data packets after exiting the lower power state.
 30. The method of claim 29, further comprising, at the first Ethernet link partner, causing a media access controller (MAC) of the first Ethernet link partner to enter a lower power state from an active state.
 31. The method of claim 29, further comprising receiving a message from the second Ethernet link partner to prevent the first Ethernet link partner from transmitting data packets; and wherein the causing the PHY to enter a lower power state and the enqueuing occur in response to the message.
 32. The method of claim 29, further comprising: at the second Ethernet link partner: preventing the first Ethernet link partner from transmitting data packets for a certain amount of time; and in response to the preventing, entering a lower power state.
 33. The method of claim 29, further comprising at the first Ethernet link partner determining an Ethernet transmission link speed based on the amount of data to transmit and the energy consumed by operating at different transmission speeds.
 34. The method of claim 33, wherein the determining the Ethernet transmission link speed further comprises determining based on an amount of energy consumed during an idle transmission period.
 35. The method of claim 29, wherein the maintaining the Ethernet link comprises reducing the amount of time to reenter an active state compared to the amount of time to reenter an active state if the Ethernet link were not maintained.
 36. An apparatus, comprising: a media access controller; a PHY; and logic to cause the PHY to enter a lower power state from an active state, wherein the lower power state consumes less power than the active state but maintains the Ethernet link to an Ethernet link partner; enqueue data packets for transmission to the Ethernet link partner via the link while in the lower power state; and transmit the enqueued data packets after exiting the lower power state.
 37. The apparatus of claim 36, wherein the logic further comprises logic to cause the media access controller to enter a lower power state from an active state.
 38. The apparatus of claim 36, further comprising logic to receive a message from the Ethernet link partner to prevent the apparatus from transmitting data packets; and wherein the causing the PHY to enter a lower power state and the enqueuing occur in response to the message.
 39. The apparatus of claim 36, further comprising logic to: preventing an Ethernet link partner from transmitting data packets for a certain amount of time; and in response to the preventing, entering a lower power state.
 40. The apparatus of claim 36, further comprising logic to determine an Ethernet transmission link speed based on the amount of data to transmit and the energy consumed by operating at different transmission speeds.
 41. The apparatus of claim 40, wherein the logic to determine the Ethernet transmission link speed further comprises determining based on an amount of energy consumed during an idle transmission period.
 42. The apparatus of claim 40, wherein the logic to maintain the Ethernet link comprises logic to reduce the amount of time to reenter an active state compared to the amount of time to reenter an active state if the Ethernet link were not maintained. 